Preparation method, device and application of walnut shell structure rich in microporous phenolic resin-based carbonaceous porous material

Abstract

This application relates to the field of porous carbon material preparation and application technology, and discloses a method, equipment, and application for preparing phenolic resin-based porous carbon materials with a walnut shell structure rich in micropores. The method includes: emulsifying and polymerizing a phenolic source, an aldehyde source, a ZnCl2-containing molten salt system, and a catalyst in an aqueous phase to obtain resin microspheres encapsulated with molten salt; after curing and oxidation treatment, in-situ activation is performed using the liquid-phase template effect of the molten salt phase under a medium-temperature inert atmosphere; after washing and desalting, high-temperature secondary etching is performed using alkali, steam, or carbon dioxide to create pores. This method utilizes a synergistic strategy of in-situ molten salt doping and hierarchical etching to effectively suppress carbon skeleton shrinkage and significantly improve microporosity. The resulting material exhibits a walnut shell-like texture on the surface, with a specific surface area of ​​1800-2600 m² / g and a micropore volume fraction >90%, exhibiting excellent electrochemical performance as a silicon-carbon anode substrate for lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of porous carbon material preparation and application technology, specifically to the preparation method, equipment and application of phenolic resin-based porous carbon material with micropores in walnut shell structure. Background Technology

[0002] Phenolic resin-based porous carbon materials have broad application prospects in adsorption separation, catalyst support, and new energy storage due to their high carbon residue ratio, controllable molecular structure, and good chemical stability. Especially in silicon-carbon anode materials for lithium-ion batteries, the porous carbon framework, as a carrier for nano-silicon, plays a crucial role in buffering the volume expansion of silicon during charging and discharging and maintaining the integrity of the electrode structure.

[0003] However, during the high-temperature carbonization process of traditional phenolic resin microspheres, significant volume shrinkage often occurs due to further cross-linking and polycondensation of polymer chains and the escape of small volatile molecules. This shrinkage causes the collapse or closure of the original pore structure inside the precursor, resulting in a low specific surface area of ​​the final carbon material and difficulty in forming a rich and interconnected microporous network. To improve the pore structure, existing technologies mainly employ physical mixing activation or hard template methods. Physical mixing activation typically involves mechanically mixing the cured resin spheres with a solid activator followed by high-temperature treatment. However, due to the diffusion resistance at the solid-solid interface, the activator cannot penetrate deeply into the microsphere core, leading to a gradient distribution of activation levels from the outside to the inside of the microsphere. This easily results in excessive surface ablation while the interior remains dense and pore-free, making it difficult to obtain a material with uniform structure and high microporosity.

[0004] On the other hand, while the hard template method can construct ordered channels by introducing nanoparticles such as silica, this method has a cumbersome process, and the subsequent removal of the template usually requires the use of highly corrosive reagents such as hydrofluoric acid. This not only increases the preparation cost and environmental risks but also easily damages the mechanical strength of the carbon skeleton during etching. In addition, a single pore-forming strategy often makes it difficult to precisely control the pore size distribution, resulting in an excessively high proportion of macropores or mesopores in the prepared carbon material, reducing the tap density of the material and failing to meet the dual requirements of high energy density lithium-ion batteries for anode substrate materials with both high micropore capacity and high structural stability. Therefore, it is particularly urgent to develop a simple process for preparing phenolic resin-based carbon porous materials that can effectively suppress skeleton shrinkage and achieve precise control of micropore structure. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method, equipment, and application for preparing phenolic resin-based carbon porous materials with micropores in walnut shell structure. This solves the problems of micropore structure collapse, difficulty in further increasing micropore volume fraction, and limited specific surface area in the preparation process of existing phenolic resin-based carbon materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides a method for preparing a phenolic resin-based carbonaceous porous material with a microporous walnut shell structure.

[0007] The method includes the following steps performed sequentially:

[0008] Step 1: Molten Salt Emulsion Polymerization and Precursor Preparation

[0009] In a polyvinyl alcohol aqueous phase system with a concentration of 0.5-2.0 wt%, a phenol source, an aldehyde source, a zinc chloride-containing molten salt system, and dilute hydrochloric acid are mixed, wherein the molar ratio of the phenol source to the aldehyde source is controlled at 1:0.6-1.2; the amount of zinc chloride-containing molten salt system added is... Total mass of phenolic and aldehyde sources Satisfy the mass ratio relationship: The mixture is homogenized at 10,000-30,000 rpm for 3-5 minutes to form an emulsion, and then heated to 60-90℃ and held for 3-6 hours to carry out acid-catalyzed polymerization to obtain oligomer microspheres containing molten salt components.

[0010] In this process, zinc chloride acts as a Lewis acid catalyst in the condensation reaction of phenolic resins, while being dispersed in the polymer network in the form of molecules or ionic clusters, thus creating pre-defined spatial sites for subsequent pores.

[0011] Step 2: Curing and Crosslinking

[0012] Add hexamethylenetetramine to the system obtained in step one, heat to 100-150℃ and hold for 3-6 hours. At this temperature, hexamethylenetetramine decomposes to produce formaldehyde and ammonia, which promotes further cross-linking of linear or branched phenolic oligomers to form a three-dimensional network structure of cross-linked phenolic spherical resin matrix. At this time, the molten salt system is encapsulated and fixed inside the cured resin matrix.

[0013] Step 3: Oxidation stabilization and in-situ activation with medium-temperature molten salt

[0014] The resin matrix obtained in step two is placed in an air atmosphere and heated to 200-300℃ at a heating rate of 3-5℃ / min and held for 1-2 hours for pre-oxidation treatment. This causes cyclization and dehydrogenation reactions on the surface of the resin spheres, forming a thermally stable rigid framework. Subsequently, the atmosphere is switched to an inert atmosphere, and the temperature is further increased to 450-550℃ at a heating rate of 3-5℃ / min and held for 30-60 minutes. Within this temperature range, the resin matrix undergoes preliminary thermal dehydration, while the zinc chloride-containing molten salt system encapsulated inside undergoes a phase transition from solid to molten liquid. The molten salt phase generates a volume occupation effect inside the carbon precursor, acting as a liquid phase template to support the carbon framework and prevent excessive shrinkage. At the same time, the molten zinc chloride performs in-situ chemical activation on the carbon matrix, inducing the initial formation of a microporous structure.

[0015] Step 4: Washing and desalting

[0016] The product obtained in step three was cooled to room temperature and washed with deionized water until no chloride ions were detected in the washing solution. After drying, a primary porous carbon material with the inorganic salt template removed was obtained. This step removed the salt occupying the micropore channels, exposing the primary pore structure.

[0017] Step 5: High-temperature secondary etching for hole creation

[0018] The primary porous carbon material obtained in step four is placed in a high-temperature environment of 700-1000℃, and an etching medium is introduced for secondary pore-forming treatment to obtain the final walnut shell-structured phenolic resin-based porous carbon material rich in micropores. This step utilizes the reaction between carbon atoms and the etching medium at high temperature to further expand the pore size and connect closed pores.

[0019] The zinc chloride-containing molten salt system described in step one consists of zinc chloride and an auxiliary salt. The auxiliary salt is selected from one or more of lithium chloride, sodium chloride, potassium chloride, ferric chloride, calcium chloride, or magnesium chloride. The mass of the auxiliary salt... With the quality of zinc chloride Satisfy the ratio relationship: The addition of auxiliary salts is used to adjust the melting point and ionic strength of the molten salt system.

[0020] Step 5, the secondary etching and hole-forming process, adopts one of the following three techniques:

[0021] Alkali etching method: Primary porous carbon material and alkali source are mixed at a mass ratio of 1:(0.5-2.0), heated to 700-900℃ at 3-5℃ / min under an inert atmosphere and held for 0.5-2.0 hours. After cooling, acid washing and water washing are performed.

[0022] Water vapor etching method: The primary porous carbon material is heated to 700-900℃ in an inert atmosphere, and a mixture of water vapor and inert gas is introduced. The total mass of water vapor introduced is (1.0-5.0):1, and the temperature is maintained for 0.5-2.0 hours.

[0023] Carbon dioxide etching method: The primary porous carbon material is heated to 800-1000℃ in an inert atmosphere, and carbon dioxide gas with a flow rate of 50-500mL / min is introduced and kept at this temperature for 2.0-6.0 hours.

[0024] The second aspect of this invention provides an apparatus for preparing phenolic resin-based carbonaceous porous materials with microporous structures in walnut shells.

[0025] The equipment is used to perform the preparation method described in the first aspect above. Its structure includes an emulsification polymerization unit, a solidification reaction unit, a first heat treatment unit, a washing and separation unit, and a second heat treatment unit connected sequentially through a material transfer pipeline or conveying device. The emulsification polymerization unit is equipped with a high-shear homogenizer with a rated speed covering the range of 10,000-30,000 rpm, used to form a micron-scale dispersed emulsion. The first heat treatment unit adopts a heating furnace with atmosphere control function. Its temperature control system is used to support segmented temperature control. The first segment temperature control range covers 200-300℃, and the second segment temperature control range covers 450-550℃. It also has an air inlet, an inert gas inlet, and a switching valve. The second heat treatment unit adopts a furnace chamber made of high-temperature corrosion resistant material. Its operating temperature range covers 700-1000℃, and it is connected to an etching medium supply device. The etching medium supply device includes a gas flow controller or a liquid vaporization device.

[0026] A third aspect of this invention provides a phenolic resin-based carbonaceous porous material with a walnut shell structure rich in micropores.

[0027] The material is prepared by the method described in the first aspect of this invention. The material has a spherical or near-spherical microstructure and a surface exhibiting a textured surface. The physical parameters of the material satisfy the following conditions:

[0028] Specific surface area measured by nitrogen adsorption-desorption test The range is: ;

[0029] Micropore volume fraction satisfy: ;

[0030] The particle size distribution ranges from 1 μm to 5 mm.

[0031] The fourth aspect of this invention provides an application of a phenolic resin-based carbonaceous porous material with a microporous walnut shell structure.

[0032] This application allows the use of the carbonaceous porous material described in the third aspect of the present invention as a negative electrode material or a composite matrix of negative electrode materials in lithium-ion batteries. The high specific surface area and high microporosity of this material provide space for loading active materials or storing lithium ions.

[0033] This invention provides a method, equipment, and application for preparing phenolic resin-based carbonaceous porous materials with a microporous walnut shell structure. It offers the following advantages:

[0034] 1. This invention introduces a molten salt system containing zinc chloride during the acid-catalyzed polymerization stage of phenolic resin. The Lewis acid properties of zinc chloride are used to catalyze the polycondensation reaction, while simultaneously dispersing it uniformly in the form of molecules or ionic clusters and locking it in the solidified polymer three-dimensional network. This in-situ doping mechanism overcomes the problem of gradient distribution of activator inside and outside the carbon sphere caused by the traditional external impregnation method, ensuring that the activation reaction occurs uniformly inside the microsphere during the subsequent carbonization process, laying the precursor foundation for the construction of a uniform microporous network.

[0035] 2. This invention utilizes the phase change melting characteristics of the molten salt system in the intermediate temperature stage to form a liquid phase support template inside the carbon precursor, generating a volume occupation effect. This effectively suppresses the excessive shrinkage and collapse of the carbon skeleton during the thermal devolvation process and induces the formation of primary pores. Subsequently, combined with the secondary etching effect of alkali, water vapor or carbon dioxide in the high temperature stage, deep pore expansion and through-pore treatment are carried out on the basis of primary pores. This hierarchical pore-forming strategy effectively increases the connectivity and density of micropores and significantly improves the micropore volume fraction of the material.

[0036] 3. By controlling the homogeneous dispersion state of the suspension polymerization system and the anisotropic shrinkage during the carbonization process, the carbonaceous porous material prepared by this invention exhibits a unique surface texture and spherical morphology. While maintaining the overall mechanical integrity of the microspheres, this structure increases the external geometric specific surface area compared to carbon microspheres with smooth surfaces, providing richer interfacial sites for electrolyte wetting and contact with active substances, which is beneficial to improving the material transport kinetics performance. Detailed Implementation

[0037] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0038] This embodiment prepares a phenolic resin-based carbonaceous porous material with a walnut shell structure rich in micropores. The specific steps are as follows:

[0039] S1. Precursor Preparation: A 1.25 wt% polyvinyl alcohol aqueous solution was prepared as the continuous phase. Phenol and formaldehyde were added to this aqueous phase, controlling the molar ratio of phenol to formaldehyde to be 1:0.9. Subsequently, a zinc chloride-containing molten salt system and an appropriate amount of dilute hydrochloric acid were added. The zinc chloride-containing molten salt system consisted of ZnCl2 and potassium chloride as an auxiliary salt, with a KCl to ZnCl2 mass ratio of 0.6:1. The total amount of the zinc chloride-containing molten salt system added was controlled to be 1.0 times the total mass of phenol and formaldehyde. The mixture was placed in a high-shear emulsifier and homogenized at 20,000 rpm for 4 min to form an emulsion. The emulsion was transferred to a reaction vessel, heated to 75°C, and reacted at a constant temperature for 4.5 h.

[0040] S2. Curing treatment: Add hexamethylenetetramine to the system after the reaction in step S1, the amount of which is 10 wt% of the mass of phenol. Heat to 125℃ and hold for 4.5 h to cure and crosslink, to obtain a crosslinked phenolic spherical resin matrix with molten salt encapsulated inside.

[0041] S3. Oxidation and Medium-Temperature Molten Salt Activation: The resin matrix obtained in step S2 is placed in a tube furnace and heated to 250°C at a rate of 4°C / min under an air atmosphere, and held at this temperature for 1.5 hours for pre-oxidation. Subsequently, the atmosphere is switched to nitrogen, and the temperature is increased to 500°C at a rate of 4°C / min, and held at this temperature for 45 minutes to melt the internal molten salt and perform in-situ activation.

[0042] S4. Washing: After the sample has cooled to room temperature in the furnace, take it out and wash the product repeatedly with deionized water until the conductivity of the washing solution no longer changes. Filter and dry to obtain primary porous carbon material.

[0043] S5. Secondary etching for pore formation: An alkaline etching process is used. The primary porous carbon material obtained in step S4 is mixed with potassium hydroxide powder at a mass ratio of 1:1.25 until homogeneous. Under nitrogen protection, the temperature is increased to 800℃ at a rate of 4℃ / min and activated at this temperature for 1.0 h. After cooling, the product is first washed with 0.5mol / L dilute hydrochloric acid, then washed with deionized water until neutral and dried to obtain the target product. Example

[0044] This embodiment prepares a phenolic resin-based carbonaceous porous material with a walnut shell structure rich in micropores. The specific steps are as follows:

[0045] S1. Precursor Preparation: Prepare a 0.5 wt% polyvinyl alcohol aqueous solution. Add resorcinol and acetaldehyde, controlling the molar ratio of resorcinol to acetaldehyde to be 1:0.6. Add a molten salt system containing zinc chloride and dilute hydrochloric acid. The molten salt system consists of ZnCl2 and the auxiliary salt sodium chloride, with a NaCl to ZnCl2 mass ratio of 0.2:1. Control the ratio of the total amount of the molten salt system added to the total mass of the phenolic monomer to be 0.5. Homogenize at 10,000 rpm for 3 min. Then heat to 60℃ and react at this temperature for 3 h.

[0046] S2. Curing treatment: Add hexamethylenetetramine to the system at a concentration of 5 wt% of resorcinol. Heat to 100°C and hold for 3 hours for curing.

[0047] S3. Oxidation and medium-temperature molten salt activation: In an air atmosphere, the temperature is increased to 200℃ at 3℃ / min and held for 1 hour. Then, the temperature is switched to an argon atmosphere and increased to 450℃ at 3℃ / min, and held for 30 minutes.

[0048] S4. Washing: After cooling, wash with deionized water until neutral, and dry to obtain primary porous carbon material.

[0049] S5. Secondary etching for pore formation: A water vapor etching process is used. The primary porous carbon material obtained in step S4 is placed in a tube furnace and heated to 700°C under argon protection. A mixture of water vapor and argon is introduced, controlling the ratio of the total mass of water vapor introduced to the mass of the primary porous carbon material to be 1.0:1, and the activation time is 0.5 h. After completion, the water vapor is cut off, and the material is cooled in an argon flow to obtain the target product. Example

[0050] This embodiment prepares a phenolic resin-based carbonaceous porous material with a walnut shell structure rich in micropores. The specific steps are as follows:

[0051] S1. Precursor Preparation: Prepare a 2.0 wt% polyvinyl alcohol aqueous solution. Add m-cresol and furfural, controlling the molar ratio of m-cresol to furfural to be 1:1.2. Add a molten salt system containing zinc chloride and dilute hydrochloric acid. The molten salt system consists of ZnCl2 and the auxiliary salt ferric chloride, with a FeCl3 to ZnCl2 mass ratio of 1:1. Control the ratio of the total amount of the molten salt system added to the total mass of the phenolic monomer to be 1.5. Homogenize at 30,000 rpm for 5 min. Then heat to 90℃ and react at this temperature for 6 h.

[0052] S2. Curing treatment: Add hexamethylenetetramine to the system at a concentration of 15 wt% of the mass of m-cresol. Heat to 150°C and hold for 6 hours for curing.

[0053] S3. Oxidation and Medium-Temperature Molten Salt Activation: In an air atmosphere, the temperature is increased to 300℃ at 5℃ / min and held for 2 hours. Then, the temperature is switched to a nitrogen atmosphere and increased to 550℃ at 5℃ / min, and held for 60 minutes.

[0054] S4. Washing: After cooling, wash with deionized water until neutral, and dry to obtain primary porous carbon material.

[0055] S5. Secondary etching for pore formation: A carbon dioxide etching process is used. The primary porous carbon material obtained in step S4 is placed in a tube furnace and heated to 1000℃ under nitrogen protection. The atmosphere is then switched to pure carbon dioxide gas, with a flow rate of 500 mL / min and an activation time of 6.0 h. After completion, the atmosphere is switched back to nitrogen for cooling to obtain the target product.

[0056] Comparative Example

[0057] The difference between Comparative Example 1 and Example 1 is that: no molten salt system containing zinc chloride was added in step S1, and only dilute hydrochloric acid was used as a catalyst for the polymerization reaction. The remaining steps and parameters are the same as in Example 1.

[0058] Comparative Example 2 differs from Example 1 in that the method of introducing the molten salt is changed. Specifically, ZnCl2 and KCl are not added in step S1; after curing in step S2, the obtained cured resin balls are physically mixed with ZnCl2 and KCl powders according to the mass ratio in Example 1, followed by heat treatment in step S3, with all other parameters being the same as in Example 1.

[0059] Compared with Example 1, Comparative Example 3 differs in that the secondary etching and pore-forming process in step S5 is omitted. Specifically, the primary porous carbon material obtained after washing and drying in step S4 is used as the final product, and the remaining steps and parameters are the same as in Example 1.

[0060] The difference between Comparative Example 4 and Example 2 is that water vapor was not introduced in step S5. Specifically, heat treatment was performed only in an argon atmosphere at 700°C without introducing water vapor as the etching medium, and the holding time remained at 0.5 h. All other steps and parameters were the same as in Example 2.

[0061] The difference between Comparative Example 5 and Example 3 is that the molten salt system in step S1 consists only of ZnCl2 and no auxiliary salt FeCl3 is added, but the ratio of the total mass of the molten salt to the total mass of the phenolic monomer remains unchanged. The remaining steps and parameters are the same as in Example 3.

[0062] Test Example 1: Pore Structure and Particle Size Distribution Test

[0063] This test example measures the pore structure characteristic parameters and particle size distribution of the materials prepared in Examples 1 to 3 and Comparative Examples 1 to 5. The specific test steps are as follows:

[0064] The sample to be tested was placed in a vacuum degassing station and continuously degassed at 120℃ for 12 hours to remove adsorbed moisture and impurity gases from the sample surface and pores. After degassing, the sample tube was transferred to the analysis station of a fully automated specific surface area and porosity analyzer, where nitrogen adsorption-desorption isotherm tests were performed under liquid nitrogen temperature conditions. A relative pressure was selected. Calculate the specific surface area using data points in the range of 0.05 to 0.30. Select relative pressure The total pore volume was calculated by converting the nitrogen adsorption amount at 0.99. ;use The adsorption isotherm data were analyzed using a model to calculate the micropore volume. According to the formula Calculate the micropore volume fraction. Take an appropriate amount of the sample to be tested and disperse it in ethanol solvent. After ultrasonic dispersion for 30 minutes, use a laser particle size analyzer to test and record the volume average particle size of the sample.

[0065] The specific data obtained from the test are recorded in Table 1.

[0066]

[0067] Analysis of the test data in Table 1 shows that the materials prepared in Examples 1 to 3 all exhibit high specific surface areas and extremely high micropore volume fractions. This result is attributed to the liquid-phase template effect and chemical activation formed during carbonization by the zinc chloride-containing molten salt system introduced during the polymerization stage. Comparing the data of Example 1 and Comparative Example 1, it can be seen that removing the molten salt system caused the specific surface area to drop sharply from 2453 m² / g to 452 m² / g, and the micropore volume fraction to decrease to 58.3%, indicating that the lack of volume occupation and support from the molten salt component led to severe skeletal shrinkage of the phenolic resin during thermal devolvation, resulting in the collapse or closure of the pore structure. Comparing the data of Example 1 and Comparative Example 2, the specific surface area and micropore volume of Example 1 are significantly higher, confirming that the in-situ polymerization introduction method can enable the activator to be uniformly distributed within the polymer network at the molecular or ionic cluster scale, thereby achieving uniform internal activation during carbonization; while the physical mixing method is limited by the solid-solid contact interface, making it difficult for the activator to penetrate to the particle core, resulting in reduced activation efficiency and uneven micropore distribution.

[0068] The secondary etching process plays a crucial role in expanding and connecting the pores, contributing significantly to the formation of the final pore structure. Comparing the data from Example 1 and Comparative Example 3, without secondary etching, the specific surface area of ​​the material is only 1198 m² / g, and the total pore volume is 0.54 cm³ / g. This indicates that although the primary molten salt activation forms a preliminary pore network, some pores remain closed or have excessively small diameters. Example 1, through high-temperature alkaline etching, utilizes the chemical reaction between carbon atoms and the etchant to open closed pores and expand existing micropores, resulting in a more than doubling of the specific surface area while maintaining an extremely high microporosity. Similarly, comparing the data from Example 2 and Comparative Example 4, the specific surface area and pore volume of the material decrease after removing the water vapor etching medium, verifying the selective vaporization and removal of amorphous carbon by the physical etching medium at high temperatures. This effect further enriches the pore structure.

[0069] The auxiliary salt components in the molten salt system also contribute to the regulation of pore structure. Example 3, using a molten salt system composed of zinc chloride and ferric chloride, showed improved specific surface area and micropore volume compared to the single zinc chloride system in Comparative Example 5. This is because the addition of the auxiliary salt adjusted the melting point and viscosity characteristics of the mixed molten salt at high temperatures, ensuring that the molten salt maintained suitable liquid-phase fluidity within a specific carbonization temperature range, thereby more effectively wetting and penetrating the carbon precursor framework. Simultaneously, different metal ions exhibit varying catalytic graphitization or activation behaviors on the carbon matrix at high temperatures. The complex salt system, through synergistic effects, optimized the microstructure of the final carbon material, resulting in higher pore volume parameters.

[0070] Test Example 2: Electrochemical Performance Test of Lithium-ion Battery Anode

[0071] In this test example, the carbonaceous porous materials prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were used as the matrix materials for silicon-carbon anodes. Coin cells were assembled and their electrochemical performance was tested. The specific experimental steps are as follows:

[0072] First, the silicon-carbon composite material was prepared. The carbonaceous porous material to be tested was mixed with nano-silicon particles at a mass ratio of 8:2, placed in a ball mill jar, and mechanically fused at 300 rpm for 4 hours to allow the nano-silicon particles to embed into the pores of the carbon material or adhere to the surface, thus obtaining silicon-carbon composite material powder.

[0073] The electrode sheets were then prepared. The aforementioned silicon-carbon composite material, conductive agent, and binder were mixed at a mass ratio of 8:1:1. An appropriate amount of deionized water was added to the mixed powder as a solvent, and the mixture was dispersed evenly using a vacuum mixer to form an electrode slurry. The slurry was then uniformly coated onto the surface of a copper foil current collector using a coating machine, controlling the coating thickness to 100 μm. The coated electrode sheets were pre-dried in an 80°C forced-air oven, and then transferred to a 120°C vacuum oven for drying for 12 hours. The dried electrode sheets were then rolled and punched into circular pieces with a diameter of 14 mm, and the active material loading was calculated by weighing.

[0074] Finally, battery assembly and testing were performed. CR2032 coin cell half-cells were assembled in an argon atmosphere glove box with water and oxygen content both below 0.1 ppm. The prepared electrode sheet was used as the working electrode, lithium metal sheet as the counter electrode, and polypropylene microporous membrane as the separator. The electrolyte consisted of 1.0 M LiPF6 dissolved in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate, with 10 wt% fluoroethylene carbonate added as an additive. The assembled battery was allowed to stand at room temperature for 12 hours. Constant current charge-discharge tests were performed using a battery testing system, with the voltage range from 0.01 V to 1.5 V. The initial charge-discharge current density was set at 0.1 C, and the subsequent cycle test current density was set at 0.5 C. The initial reversible specific capacity, initial coulombic efficiency, and capacity retention after 100 cycles were recorded.

[0075] The specific data obtained from the test are recorded in Table 2.

[0076]

[0077] The data in Table 2 show that the materials prepared in Examples 1 to 3 exhibit high initial reversible specific capacity and cycling stability when used as silicon-carbon anode substrates. This performance is related to the high micropore volume fraction and the special walnut shell surface structure of the materials. The comparison of data between Example 1 and Comparative Example 1 shows that in a low-porosity substrate lacking a molten salt template, silicon particles cannot be effectively accommodated, resulting in an initial coulombic efficiency of only 72.4%, and a sharp drop in capacity retention to 45.2% during cycling. This confirms that the rich microporous structure constructed by in-situ molten salt and etching processes can provide the necessary buffer space for the volume expansion of nano-silicon during lithium intercalation, limiting the pulverization of silicon particles and their separation from the current collector, thereby maintaining the integrity of the electrode structure.

[0078] The in-situ polymerization method of introducing molten salt directly impacts the long-term cycling stability of the material. Comparing the data from Example 1 and Comparative Example 2, although Comparative Example 2 also introduced a salt template, its cycle retention rate was 75.4%, lower than the 92.3% of Example 1. This is because physical mixing cannot achieve uniform molecular-level dispersion of the template agent within the polymer precursor, resulting in a heterogeneous pore distribution within the final carbon material. In areas with insufficient porosity, the expansion stress of silicon particles cannot be released, leading to localized breakage of the conductive network. Conversely, the in-situ introduction mechanism of this method ensures the uniformity of the pore network, resulting in a more uniform stress distribution and improved mechanical stability of the composite material during repeated charge-discharge cycles.

[0079] Secondary etching for pore creation and the regulation of auxiliary salt components further optimized the lithium-ion transport kinetics. Comparing the data from Example 1 and Comparative Example 3, and Example 2 and Comparative Example 4, the sample treated with secondary etching exhibited higher initial coulombic efficiency and capacity retention. The mechanism lies in the fact that the high-temperature etching process removes some amorphous carbon and opens up closed pores, reducing the diffusion resistance of lithium ions within the carbon matrix and increasing the wetting channels of the electrolyte. Furthermore, the material prepared using the complex salt system in Example 3 showed better performance than the single salt system in Comparative Example 5, indicating that optimizing the microporous structure by adjusting the molten salt composition helps to construct a more robust conductive framework and reduces electrical contact failures caused by changes in the volume of active materials during cycling.

Claims

1. A method for preparing phenolic resin-based carbonaceous porous materials with microporous walnut shell structure, characterized in that, Includes the following steps: Precursor preparation: In a polyvinyl alcohol aqueous phase with a concentration of 0.5-2.0 wt%, a phenol source, an aldehyde source, a ZnCl2-containing molten salt system, and dilute hydrochloric acid are added, wherein the molar ratio of the phenol source to the aldehyde source is 1:0.6-1.2, and the amount of the ZnCl2-containing molten salt system added is 0.5-1.5 times the total mass of the phenol source and the aldehyde source; the mixture is homogenized at a speed of 10000-30000 rpm for 3-5 min to form an emulsion, and then heated to 60-90℃ and held for 3-6 hours for polymerization; Curing treatment: Add hexamethylenetetramine to the system obtained in step S1, heat to 100-150℃ and keep warm for 3-6 hours to cure and obtain cross-linked phenolic spherical resin matrix; Oxidation and medium-temperature molten salt activation: The resin matrix obtained in step S2 is pre-oxidized in air by heating to 200-300℃ at 3-5℃ / min and holding for 1-2 hours; then the atmosphere is switched to inert and the temperature is increased to 450-550℃ at 3-5℃ / min and held for 30-60 minutes to melt the ZnCl2-containing molten salt system inside the resin matrix and activate it in situ. Washing: Cool the product obtained in step S3 to room temperature, wash with deionized water until no chloride ions are detected, and dry to obtain primary porous carbon material; Secondary etching and pore-forming treatment: The primary porous carbon material obtained in step S4 is etched and pore-forming treatment at a high temperature of 700-1000℃ using alkali, water vapor or carbon dioxide to obtain a phenolic resin-based carbon porous material with a walnut shell structure rich in micropores.

2. The method for preparing phenolic resin-based carbonaceous porous material with microporous walnut shell structure according to claim 1, characterized in that, In step S1, the ZnCl2-containing molten salt system is composed of ZnCl2 and an auxiliary salt, wherein the auxiliary salt is one or more of LiCl, NaCl, KCl, FeCl3, CaCl2, or MgCl2, and the mass ratio of the auxiliary salt to ZnCl2 is 0.2:1 to 1:1; the phenol source is one or more of phenol, p-methylphenol, phloroglucinol, tert-butylphenol, cashew phenol, or resorcinol; and the aldehyde source is one or more of formaldehyde, acetaldehyde, propionaldehyde, furfural, glutaraldehyde, or benzaldehyde.

3. The method of producing a walnut shell structured microporous- rich phenolic resin-based carbonaceous porous material according to claim 1, characterized by, The secondary etching process described in step S5 employs an alkaline etching method. The specific process is as follows: the primary porous carbon material is mixed with an alkaline source at a mass ratio of 1:(0.5-2.0), and the mixture is heated to 700-900℃ at a rate of 3-5℃ / min under an inert atmosphere and held at that temperature for 0.5-2.0 hours. After cooling, the mixture is acid-washed and water-washed until neutral. The alkaline source is one or more of KOH, NaOH, Na2CO3, or K2CO3.

4. The method of producing a walnut shell structured microporous- rich phenolic resin-based carbonaceous porous material according to claim 1, characterized by, The secondary etching process described in step S5 uses a water vapor etching method. The specific process is as follows: the primary porous carbon material is heated to 700-900°C in an inert atmosphere, and a mixture of water vapor and inert gas is introduced. The total mass of water vapor introduced is (1.0-5.0):1, and the temperature is maintained for 0.5-2.0 hours.

5. The method of producing a walnut shell structured microporous- rich phenolic resin-based carbonaceous porous material according to claim 1, characterized by, The secondary etching process described in step S5 uses carbon dioxide etching. The specific process is as follows: the primary porous carbon material is heated to 800-1000℃ in an inert atmosphere, and carbon dioxide gas with a flow rate of 50-500mL / min is introduced by switching the atmosphere and keeping it at that temperature for 2.0-6.0 hours.

6. A device for preparing phenolic resin-based carbon porous materials with microporous walnut shell structure, used to implement the method for preparing phenolic resin-based carbon porous materials with microporous walnut shell structure according to any one of claims 1-5, characterized in that, It includes an emulsification polymerization unit, a curing reaction unit, a first heat treatment unit, a washing and separation unit, and a second heat treatment unit connected in sequence. The emulsification polymerization unit is equipped with a high-shear homogenizer with a rotation speed of up to 30,000 rpm; The first heat treatment unit is a tube furnace or rotary furnace capable of atmosphere switching, with a temperature control range covering 200-550℃. The second heat treatment unit is a high-temperature corrosion resistant furnace with a temperature control range of 700-1000℃, and is equipped with a gas flow controller or solid feeding device for introducing etching medium.

7. The equipment for preparing phenolic resin-based carbonaceous porous materials with microporous walnut shell structure according to claim 6, characterized in that, The first heat treatment unit is equipped with a tail gas treatment device for recovering the components generated by the volatilization of the ZnCl2-containing molten salt system in step S3; the washing and separation unit is connected to an ion concentration detector for monitoring the chloride ion concentration in the washing liquid.

8. A phenol formaldehyde resin-based carbonaceous porous material rich in micropores of a walnut shell structure, characterized by, The material is prepared by the preparation method according to any one of claims 1 to 5, and the specific surface area of ​​the material is 1800-2600 m² / g, and the micropore volume fraction is >90%.

9. The walnut shell structure-rich microporous phenolic resin-based carbonaceous porous material according to claim 8, characterized in that, The material has a particle size distribution range of 1μm-5mm and a surface exhibiting a walnut shell structure with an uneven texture.

10. The application of a phenolic resin-based carbonaceous porous material with a walnut shell structure rich in micropores as described in any one of claims 8-9 in silicon-carbon anode materials for lithium-ion batteries.